Shipping depends on how well you want the comics packed, and on how much the total weight is.
Airmail start at $2 and goes to $15 for 1 kilo (>2 lbs.).
You optimize the shipping cost if the weight is slightly below 2 kilos or below 10 kilos.

2 kilos equals:

4-5 comic size tp:s like Preacher or Sandman, or

6-7 manga collections like Blade of the Immortal and Oh My Goddess, or